Purification of hydrocarbons



Nov. 5, 1940. f w. R, woon 2,220,138

PURIFICATION OF HYDROCABBONS v Filed June l0, 1938 HOLVALLQVBH PUR\F\EDLIQLHD HYDROCAR BON 33 SEPARATOR SOLUTION oF swRoNG ALKALI BOLVALLDVBHLIQUID HYDRocARBoN FREE oF H25 SEPARATOR' SOLUTION OF WEAK ALKAL\ Z O (DE 98 :fr w Q. S

INVENTOR MMM/ff@ ATTORNEYS Patenti-,rl Nev. s, 1940 PUItIFICATIQN FHYDROCARBONS wllllm nobel-a wood, Louisville, xy., asslxnor to TheGirdler Corporation, Louisville, Ky., a

corporation of Delaware Applicatloninne 10, 1938, Serial N o. 212,929

3 Claims. (CL 196-32) 'Ihis invention relates to the treatment ofhydrocarbon compounds in liquid state for'the removal of sulfurcompounds therefrom.

The sulfur impurities commonly'found in hy- 5 drocarbons particularlythose obtained from petroleum oils, may include hydrogen 'sulilde lwhich vmay be that derived from the original petroleum oil or asa resultof certain reactions employed in the refining processes, andparticularly in the cracking process. Hydrogen sulilde is of a stronglyacidic nature and may be removed from such hydrocarbon liquids byreacting it with an agent of 'an alkaline nature. However, the reactionbetween a strongly acidic u material such as hydrogen sulfide, and astrongly alkaline inorganic material such as caustic soda or the like,results in a relatively stable by-product from which the hydrogensulfide cannot be readilyremoved in gaseous form to regenerate thealkaline reagent.

Other sulfur compounds commonly found in such hydrocarbon liquids aremercaptans, which are of a weak acidic character and form readilydecomposable compounds with 'alkaline treating agents. 'I'he by-productresulting from the rehas reacted with the hydrogen sulfide cannot bereadily regenerated for reuse. If a weak alkaline agent be employedwhich will react with the hydrogen sulde to form a readily decomposable40 by-product, it will not necessarily react with all of the weaklyacidic mercaptans. Thus, if a strong inorganic alkali be employed nocyclic system can be employed, since large quantities cf sodium sulfide,which .cannot be regenerated are formed when soda is used as thealkaline material, and if a weakly alkaline agent be employed there isno assurance of complete removal lof the mercaptans.

It has been proposed in the Bottoms Reissue Patent 18,958, to usealkaline amines for removing sulfur compounds from gaseous mixtures, andin a cyclic system, and this has proved very eilicient and satisfactoryin commercial practice, but due to the special problems involved in thetreatment of liquid hydrocarbons it has not been thought practicable toemploy such alkaline amlhesin the treatment of. lliquid hydrocarbons.

Although alkaline amines of the concentration recommended in the Bottomsreissue patent, 5

' namely about 50%; are not practical for remov- 'lution and the liquidtherefore becomesproporing sulfur compounds from liquid hydrocarbons,

it has now been discovered that hydrogen sulfide may be effectively andsatisfactorily removed by the use of an alkaline amine of com- 10paratively low concentration, and circulated in a cyclic system withregeneration and liberation of the sulfur compound.

It has been further discovered that where the liquid hydrocarboncontains both hydrogen sul- 15 de and mercaptans, the hydrogen sulfidemay be first removed by an alkaline -amine ilowing in a cyclic systemwith regeneration, and that thereafter the mercaptans may be removed byla stronger alkaline reagent, which due to the weak acidic character ofthe mercaptans, may be readily regenerated so that the alkaline reagentmay here also ow in a cyclic system with regeneration.

By using two separate closed treating cycles employing basic agents andoperating in succession on the liquid hydrocarbon these sulfur compoundsmay be removed without the development of stable by-products, and withregeneration of the basic agents in both cycles. 'I'he strongly acidicsulfur compound is removed by the solution of a weakly alkalinecompound, andthe weakly acidic sulfur compound is removed by a solutionof a strongly alkaline compound.

It has been further discovered that by the use of dilute solutionscontaining less than 30% of the `amine base, and preferably in the formof monoethanolamine, the amine solution saturated with hydrogen sulfidewill have a lower viscosity than the fresh solution, and a readyseparation of the saturated solution from the liquid hydrocarbon can Foeeffected. Furthermore, the solution containing hydrogen suliide has ahigher `specific gravity than the fresh so- 45 ti'onatelyl heavier thanthe liquid hydrocarbon which also assists in the separation.Furthermore, the solution saturated with hydrogen sulde has a greatersurface tension than the fresh solution and therefore less tendency toemul- 50 sify. Heretofore danger of emulsication of Vorganic alkalinematerials with the liquid hydrocarbons has been` considered an obstacleto the usev of such materials. Thus, the results obtained by the use ofairline solutions of comapparatus utilizing difference in speciiicgravity` or the separator Il. 60

paratively low concentration are contrary to prior teachings to theeffect that the emcient operation required relatively concentratedsolutions of about 50% or more oi the amine.

'I'he present process may be carried out in various types of apparatus.In the accompanying drawing there is shownsomewhat diagrammatically atype of apparatus which may be employed. The liquid hydrocarbon, forinstance a prime cut naphtha or a virgin naphtha, may be deliveredthrougha pipe I0 into a mixing chamber Il in which it is thoroughlymixed with an amine solution which is immiscible therewith, anddelivered through the pipe I2. The two liquids may iiow in the samedirection and intermixing may be eiected in Aany suitable manner, as forinstance by bailles or by mechanical agitation, or by means effectingrepeated changesin the direction of iiow through the mixer. The aminewill react with the hydrogen suliide and the mixture of liquidhydrocarbon. and amine saturated with hydrogen suli'lde may pass outthrough the pipe I3 to any suitable form of separator Il. The separationmay be eilected by the difference in specific gravities of the twoliquids, and by a mere settling process, or the separator may be in theform oi.' a centrifuge or any other type oi for effecting separation.The lighter liquid hydrocarbon free. of hydrogen sulfide may be drawn oifrom the top of the separator through the pipe I5, and into the secondstage of the'process in the event that it contains mercaptans, but ii itis free of mercaptans the liquid hydrocarbon free of hydrogen sulfidemay be delivered from the pipe I5 through the pipe I6 to any desiredpoint of disposal.

'I'he solution of the relativelyweak amine saturated with hydrogen suldemay be returned from the separator Il through a pipe I'I into areactivator I8 where the liquid is heated or subjectedtojsub-atmospheric pressure, to remove the hydrogen sulfide in gaseousform through the vent I9. 'I'he reactivator may be of the `type shown inthe Bottoms patent above referred to. Thereactivated and puriiied aminesolution may be delivered through a pipe 20 by means oi' a pump 2| andback through the pipe I2 entering the mixing chamber II, and this pipeI2 may include -a cooler I2' for removing the heat imparted to theliquid by the heating coil I8 in the reactivator I8.

It is unnecessary to employ any `ash drums or the like iorl preventingthe liquid hydrocarbon from entering the reactivator I8, since it is notnecessary to conduct the process at elevated temperatures or pressures,and no loss of the amine results .from vvaporization in the reactivatorI8 Thus a very economical process results.

Assuming that .the liquid hydrocarbon to be treated contains bothhydrogen suliide and mercaptans, the liquid hydrocarbon may be treatedas above described by the amine solution which will remove the highlyacidic hydrogen suliide without removing appreciable quantities of theweakly acidic mercaptans, most of which will remain in the liquidhydrocarbon passing through the outlet pipe I5.

The liquid hydrocarbon may then be delivered to the second phase of theprocess which may be carried ,out by apparatus very similar to thatemployed in the rst phase. The liquid hydrocarbon'free of hydrogensulfide, and containing the mercaptans, will ilow through the pipe 38 toamixing chamber-3l whereitismixcdwltha solution oi' any stronglyalkaline inorganic material entering through the' pipe 32. The stronglyalkaline material may be a 15% solution ot caustic soda, which isimmiscible therewith and which 5 will react with the mercaptans, and themixture of the alkaline solution saturated with mercaptans and theliquid hydrocarbon may be delivered through a pipe 3l to a. separator3l. The two liquids will separate byl gravity in the separator 1o 3l, ormay be separated mechanically by a omtrifuge, and the purined liquidhydrocarbon will be delivered through the pipe 35. The alkaline solutionsaturated with the mercaptans may be drawn on through the pipe 31 anddelivered to 15 a reactivator 38 heated by 'a coil 3l'. 'I'he mercaptanswill be volatilized and delivered in gaseous form through the vent 38,and the reactivated alkaline solution returned through the pipe Il Vandpump 4I to the pipe 32 which may contain 20 a cooler 32'.

By means of the present process liquid hydrocarbons may be treatedwithout requiring a. prior gasiiication stage, .and the puriiication maybecarried out at low temperature and at a low cost. It is not necessaryto employ high treating temperatures, which is frequently foundnecessary in the treating of gaseous hydrocarbons where there is presentthe danger of condensation.

The process is very economical, due to the i'act 30 that little, if any,of the amines or alkaline solutions are lost, and there is noappreciable amount of hydrocarbon lost in the solution going to thereactivator. This is due in large measure to the use of a relatively lowconcentration of amine-35 instead of the higher concentration heretoforedisclosed for the treatment of mixed gases.

Reference has been made to monoethanolamine as the preferred weaklyalkaline material. The term amineas used in this case is intended to 40include any of the other amines or analogous organic bases dened in theBottoms patent above referred to as an amine selected from the group`consisting of aliphatic and cycloparaiiin amines,

'and which is free from carboxyl or carbonyl 45 groups, and which has aboiling point not substantially below 100 C. l Any of these may beemployed within the scope of the present invention. The amine employedis preferably an aliphatic amine, and preferably one including ahydroxyl group, such amines being known as allqlol amines. Y

In the speciiic example given there is reference to the use of naphtha,but any other appropriate type of liquid hydrocarbon which has adistinctly different 'speciiic gravity from the alkaline solution may beemployed, such for instance, as kemsene, gasoline, or the like.Furthermore, the invention may be employed in the treatment ofhydrocarbons in liquid state under pressure con- 00 ditions suiiicent tomaintain normally gaseous hydrocarbons in liquid condition during thepln'iflcaton of the same. As will be apparent, othery iorms andarrangements of apparatus may be made for carrying out the inventionwithout departing from the scope of the same.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. The process of removing sulfur compounds 7o from liquid hydrocarbonsand separately recovering weakly acidic sulfur compounds and stronglyacidic sulfur compounds in gaseous form, which includes first mixing thehydrocarbon in a liquid State with a solution containing not more than30% alkylol amine and insuiliciently basic to react in a substantialmeasure with mercaptans and other lweakly acidic sulfur compounds insaid hydrocarbon, but suihciently basic to react with hydrogen sulde andother strongly acidic sulfur compounds therein, separating saidhydrocarbon and said solution, thereafter mixing said hydrocarbon in aliquid state with a solution of an alkali suiliciently basic to react insubstantial measure with mercaptans and other weakly acidic sulfurcompounds in said hydrocarbon, separating said hydrocarbon and saidsecond mentioned solution, and separately heating said solutions toliberate therefrom the strongly acidic sulfur compounds and the weaklyacidic sulfur compounds in gaseous form and regenerate the solutions.

2. The process of removing sulfur compounds from a hydrocarbon in aliquid state, which includes maintaining a cyclic flow of a solutioncontaining not over 30% of an alkylol amine through a contact chamber, aseparator and a heated regenerator, maintaining a separate cyclic ow ofa solution of a strong alkali through a contact chamber, a separator anda heated regeneratorand circulating a hydrocarbon in liquid 26 statethrough said contact chamber and separator of the :Erst cycle, and thenthrough the contact chamber and separator of the second cycle, toseparate the strongly acidic sulfur compounds from the hydrocarbon inthe rst cycle and weakly acidic sulfur compounds from the hydrocarbon inthe second cycle and to deliver the strongly acidic sulfur compounds andthe weakly acidic sulfur compounds in gaseous form and separately fromsaid heated regenerators.

3. The process of purifying hydrocarbons in a liquid state andrecovering hydrogen sulfide and mercaptans separately in gaseous form,which includes passing the liquid hydrocarbon in contact with a solutionof an alkylol amine of a concentration not over 30%, to thereby removefrom the liquid hydrocarbon the hydrogen sulde present, separating theliquid hydrocarbon from the solution, mixing the liquid hydrocarbon witha solution of a strong alkali to thereby remove the mercaptans,separating the hydrocarbon from said last mentioned solution, andseparately heating said solutions to separate therefrom the hydrogensulilde and the mercaptans in gaseous form and regenerate saidsolutions.

wnmAM ROBERTS woon.

